Tanning process.



W. S. SHAW.

TANNING PROCESS. {\PPLICATION FILED SEPT. 10. 1914.

Patented Au 10, 1915.

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WILLIAM S. SHAW,,OF BOYNE CITY, MICHIGAN.

TANNING PROCESS.

To all whom it in 1/ concern Be it known that I, WiLLIAM S. SHAW, a citizen of the l'nited States, residing at Boyne City, in the county of Charlevoix and State of Michigan, have invented certain new and useful Improvements in Tanning Processes, of which the following'is a specification.

My invention relates to improvements in processes in which the period of time consumed in tanning hides is reduced to a minimum by subjecting the hides to the influence of combined heat and boiling in vacuum while they are immersed in the tanning solution.

It has been proposed heretofore to shorten the usual time of tanning by the ordinary cold process, by theapplication of moderate degrees of heat to the tanning solution, and sometimes by sealing the vats and subjecting them to ,a vacuum or partial vacuum,

and sometimes by combining the two features of'heat and vacuum. So far as I am aware, however, it has been heretofore universally believed that subjecting the hides to the action of boiling for any considerable period of time was objectionable and would inevitably result in detrimentally affecting the hides. In the patent to Nance No. 1,065,168 it is proposed to effect a shortening of the time of tanning by bringing the tanning solution. to the boiling point momentarily at intervals; the suggestion being that even such momentary, intermittent boiling must be in the presence, or under the condition of, an extremely high vacuum, so that the temperature is maintained very low.

, This Nance process is in conformity with the understanding that continued boiling is detrimental, and especiallydangerous if effected at any temperature above that which corresponds to an almost perfect vacuum.

I have discovered that, contrary to the general belief heretofore existing, hides may be subjected to continuous boiling in ordinary tanning solutions for extended periods of time without injury, even though the temperature be considerably higher than that represented by a very high vacuum, provided, the process be conducted under proper conditions, such for example as those hereinafter described.

Important results of my discovery are, first, that I am enabled to take advantage of Specification of Letters Patent.

Patented Aug. 10, 1915.

Application filed September 10, 1914. Serial N 0. 860,975.

from extended boiling, as distinguishedfrom a mere momentary intermittent boilmg, and, secondly, I am enabled to conduct the tanning process under such a moderate degree of vacuum as is readily obtained and maintained in commercial practice without employing highly refined vacuum-producing apparatus. v

Figure 1 is a plan view of one preferred form of apparatus which I employ for carrying out my improved process; and Fig. 2 is an elevation of Fig. 1.

In a simple form, my process may be car ried out by subjecting a single batch of hides to one or more extended periods of boiling in a tanning solution of proper strength and under such degree of vacuum that the boiling temperature shall not rise too high, es pecially during the earlier stages of the tanning, but I prefer to carry out my process as a continuous operation, in which several batches of hides are successively subjected to the action of tanning liquor of different strengths and to varying temperatures and corresponding air pressures. This preferred process is described as follows: To

carry out such process I provide a series of tanks. These tanks communicate with eachcurately adjusted. The vacuum in the tanks is maintained by a suitable exhaust airpump which is connected in multiple to all of the tanks through a common header between which and each tank is interposed a needle valve for the purpose of adjusting the degree of vacuum in each tank. The tanning solution is in all cases admitted to the final tank of the process and is circulated through the entire series of tanks until it reaches the initial tank of the process in which the green hides have been placed preparatory to tanning.

Referring to the drawings, 3 represents a suitable tank containing the strong tanning solution, this tank communicating with each of the vacuum tanks A, B, C, D, E, F, G, H, J and K of thepprocess by means of a common pipe and short pipe connections 5 and valves 6 between each of the tanks and the said common pipe 4. The proper degree of vacuum in each of the tanks is maintained by suitable exhausting apparatus, which may preferably include a condenser connected with a'common leader 7, the latter communicating with each tank through azpipe and a valve. 8 which may be suitably adjusted so as to reduce the air pressurein each tank to the required amount. A suitable steam boiler (not shown) sup plies steam to the header pipe 9 which is itself connected to the common main 10, the latter having branches and valves 11 therein leading to steam coils 12 in the bottom of each tank of the series. The valves 11 are of any suitable type that may be adjusted to regulate the temperature of each of the tanks to the proper degree.

Assuming that the process and apparatus have been in use for some time and that the continuous character of the process has been established, the following may be taken as an example of the manner in which the process is carried out and the condition of the hides and apparatus during any step in the process. In the drawings I have shown a battery of ten tanks, it being understood, however, that more or' less tanks maybeused, depending upon the time necessary to carry out the tanning process. Each step of'the process covers a length of time suflicient to effect a certain stage of the tanning, twenty-four hours being the length of time which I have selectedin this case for each stage of the process, although it is obvious that under certain conditions and with certain classes of hides this length of time may be made longer or shorter. Allowing one empty tank for taking out the tanned hides and replacing them with a fresh supply of green stock, the apparatus shown effects a complete tanning of the hides in nine periods of twenty-four hours each; that is to say, nine days between the insertion of the supply of green stock and the removal of the tanned hides. Ve will assume in this case that the hides in the tank A are undergoing the final step in the tanning process and that the solution is traveling in the direction of the arrow 13. It is understood that the strong tanning solution is admitted to the tank A through the valve 6, and during this time the valve 14 in the lower pipe connecting the tanks A and K is closed, as is also the similar Valve 14 connecting the tanks K and J. The tank K in this case is the one from which the tanned hides are being removed preparatory to the insertion of a supply of green stock, while the tank J contains a supply of green stock to which the weak tanning solution has been admitted through the valve 14 connecting the tanks J and H. It should be understood that while the process of tanningis going on, the'valves 14- connecting the tanks A, B, C, D, E, F, G, H and J may be each opened slightly if desired so as to maintain the proper level of tanning solution in each tank of the series, the total deficiency being made up by gradually admitting strong liquor to the tank A from the supply tank 3. As before referred to, the degree of vacuum in the tank J which I have assumed to be the one containing the green hides being initially treated, is the tank in which there is the highest degree of vacuum, while the tank A, containing the strong liquor and the almost completely tanned hides, is maintained at a higher temperature and a correspondingly less degree of "acuum than the tank J. The diflerence in the pressure of the various tanks is sufficient to cause the solution to circulate through the series, but, if desired, a circulating pump or pumps may be used to effeet a more positive flow of the liquor.

In the particular'example' of the process and apparatus which I am describingthe initial tank J in which are the green hides, is maintained at a temperature of between 72 F. and 75 F., and in order to effect a boiling of the solution the "acuum is held at approximately twenty-nine inches of mercury. It should be understood that since the tanning solution inthe initial tank J is com- ,paratively weak, the boiling temperature and pressure approximate more nearly to those of pure water than would be the case if this tank was filled with strong liquor which boils at a considerably higher temperature. Thus, I am enabled to effect a boiling of the solution inthe tank J at this low temperature with a much less perfect vacuum than would be necessary if a strong solution were employed at the commencement of the process. It is of course understood that the ebullition of the tanning liquor is of benefit principally in thoroughly stirring up and circulating the solution,

since the prime object in subjecting the hides to the influence of a vacuum and heat is to drive ofl the water contained in the inner cells of the green hides, and thus the real determining factor is the boiling point of water under a given condition of vacuum. The degree of vacuum isreduced. and the corresponding absolute air pressure thus increased in the tanks H,'G, F, E, D, C, B and A by suitably adjusting the valves 8 leading to the said tanks, the change in pressure between the various tanks being suitably graduated so that'in'the final tank A of the process the degree of vacuum which is present runs in the neighborhood of twentysix inches. It is manifest that in order to cause ebullition in the said tanks H, G, etc., it is necessary to raise the temperature considerably higher than that of the tank J, the temperature gradually increasing in the different stages of the process until when the final tank is reached a temperature of in the neighborhood of 130 is used.

The principle of operation is manifest from the above description of the process. When the hides are green they contain practically nothing but water occluded in their cells and pores, and it is necessary to cause the removal of this water before tanning solution can enter to take .its place and have its effect in changing the hide into leather. Until the hide has been partially tanned by the introduction of weak tanning solution into the cells and pores, a high temperature is highly injurious, but after the hide has been charged with a Weak solution it is then safe to increase the strength of the tanning liquor, increase the temperature; and thus boil out the Weak solution from the pores of the hides so as to admit the heavier tan'- ning liquor; the process being repeated as -nany times as there are tanks or stages in the'tanning process, until the strongest tanning liquor has been caused to enter the pores and cells of the hides and thus effect the proper chemical and physical changes to complete the tanning process. It is of course understood that as soon as thehides have undergone the final stage of the process in the chamber A, the valve 14 connecting the tanks A and B is closed, the valve 1 L connecting the chambers K and J is opened, and the flow of strong liquor is changed from the chamber A to the chamber B by actuating the val es 6 leading to the said tanks. The liquor in the tank A is then returned to the storage tank 3 and the tanned hides removed preparatory to the introduction of a. fresh supply of green stock. The tank A then being the idle one in the series, tank K becomes the initial tank in the process, and its temperature and pressure and those of the other tanks in the chain are adjusted to meet the new conditions. This operation is repeated every day until the tank J becomes the final tank in the process and the tanning of the hides therein thus completed.

1 One of the principal advantages of the continuous boiling of the liquor resides in the fact that in the ordinary operation of tanning the solution becomes materially Weaker on account of the consumption of tanning material by the hides. In my process the boiling of the liquid automatically strengthens the solution as the latter gets Weak and provides room for the admission of strong liquor as the tanning proceeds.

In all of the vacuum tanning processes With which I have had experience in the past the constant aim and effort have been to reduce the length of time necessary for tanning by simply subjecting the solution and hides to as high a vacuum as possible, but in all of the prior art processes I have found that after a certain degree of vacuum has been reached it'is not practical to reduce the air pressure any further on account'of the enormous initial outlay required to provide exhaust pumps capable of maintaining this high vacuum and the great expense in keeping them in operation continuously while the process is being carried out. Thus, the old processes are usually a compromise between the advantages and benefits resulting from. the use of a high vacuum and the trouble and expense in the maintenance of such vacuum.

In my process the time required to properly tan the hides is very much less than that required by any other method heretofore known, as will be apparent when it is considered that after the initial treatment of the hides to render them immune to the action ofhigh temperature during which time the vacuum is most pronounced, the

.hidesare then boiled in a strong liquor at in following out different steps of the process rather than a detailed representation of the apparatus actually used in practice, and it should be understood by those skilled in the art that the apparatus may be changed to suit individual needs and certain details of the process may be similarly modified Without departing from the spirit of the invention, and thus I do not limit myself by I the description of the process and apparatus given above, except in so far as specified in the appended claims.

I claim 1. The process of tanning hides, which consists in immersing them in a tanning solu tion and subjecting both the solution and the contained hides to a protracted period of pronounced uninterrupted boiling under a reduced vapor pressure, whereby the boiling is effectedat a temperature low enough to avoid injury to the hides, and the ebullition of the solution induces an effective circulation thereof.

2. The process of tanning hides, which consists in immersing them in a tanning solution, establishing a vacuum over the latter,,

and causing the solution to boil continuously until the tanning is complete and at a temperature low enough to prevent injury to the hides.

3. The process of tanning, Which consists in initially'subjecting the hides to the action of consists in immersing them in a weak tanning solution, reducing the air pressure low,

enough to cause the solution to boil at a temperature low enough to prevent 1H]l1Iy to the green hides, and subsequently increasing the strength of the tanning solution as the tanning process proceeds.

5. The process of tanning hides, which consists in immersing them in a tanning solution, reducing the air pressure low enough to cause the solution to boil continuously at a temperature low enough to prevent injury to the green hides and for a period sufficient to partially tan the hides, and-subsequently continuing the boiling while the air pressure and temperature are increased by successive graduated stages until the hides are completely tanned.

G. The process of tanning hides, which consists in immersing them in a tanning solution, reducing the air pressure low enough to cause the solution to boil continuously at a temperature low enough to prevent injury to the green hides and for a period suflicient to partially tan the hides, and then boiling the hides at air pressure and temperature increased by successive graduated stages until the hides are completely tanned,

the strength of the tanning solution being gradually increased as thetanning proceeds.

7. The process of tanning hides, which consists in initially subjecting them to the action of a boiling tanning solution at a temperature not greater than 7 5 F. with a corresponding degree of vacuum as the first step in the process, and then continuing the boiling of the hides in the tanning solution in successive stages in which the air pressure and temperature are successively increased until the final temperature at the end of the process and when the tanning is complete, reaches in the neighborhood of 130 F.

8. The process of tanning hides, which consists in initially subjecting them for an extended period to the action of a boiling tanning solution at a temperature not greater than 75 F. with a corresponding degree of vacuum as the first step in the process, and then continuing the boiling of the hides in the tanning solution in successive stages in which the air pressure and temperature'are successively increased until thefinal temperature at the end of the process and when the tanning is complete, reaches in the neighborhood of 130 F., the strength of the tanning solution being pro gressively increased as the tanning proceeds.

WILLIAM S. SHAlV.

\Vitnesses:

E. G. Goonwm, L. G. MALONE. 

